The work on uptake of ionic iron by mouse peritoneal macrophages, now in progress, will be concluded. The requirements for and the rapidity of the iron uptake, as well as the conditions which affect uptake will be investigated. During the next year the effect of various chelators on loss of iron from iron loaded macrophages will be studied. Among the iron chelators to be used will be desferrioxamine and bipyridyl. Desferrioxamine will be isolated from streptomyces pilosus and deironized. The compound will be radiolabelled with C14 and H3 and radioisotopic localization in macrophages. Both autoradiography and cell fractionation techniques will be employed.